1. Field of the Invention
The present invention relates to ink jet printers having multiple print heads, and more particularly to a cover for an alignment sensor that facilitates alignment of one of the multiple heads to others of the multiple heads.
2. Description of the Related Art
Ink jet printers have become an extremely popular format for achieving high quality computer printout at low cost. Ink jet printers form a printed image by ejecting small ink droplets from a print head in predetermined patterns onto a recording medium. The print head is mounted on a moveable carriage which provides right and left reciprocal movement at high scanning speeds across the width of the recording medium, while the recording medium is slowly fed in the lengthwise direction.
Recently-introduced ink jet printers have multiple print heads, such as two or more print heads mounted on the reciprocating carriage. The print heads may be identical to each other, such as a dual black or dual color print heads which increase black and white or color printout speeds by up to a factor of two. Alternatively, the print heads may differ from each other, such as a black print head paired with a color print head which provides good color reproduction without sacrificing print speed for black and white documents. As a further example, some ink jet printers are equipped with one full color print head paired with a photographic-density color print head, so as to achieve high quality photographic-like printout.
One complication introduced by providing ink jet printers with multiple print heads is the need to align printout for one of the multiple print heads to all others of the multiple print heads. Without alignment, mechanical manufacturing tolerances would cause printout from one print head to be mismatched relative to printout from others of the print heads.
Some existing multiple head ink jet printers utilize a manual alignment technique in which predetermined patterns are printed and the computer user is asked to respond to questions concerning quality and appearance of the printout. Such techniques are not generally satisfactory, in that they cause needless user confusion, result in inconsistent alignment accuracy, and inevitably complicate the printer.
The assignee of the present application has recently described a technique for automatic alignment of multiple print heads in an ink jet printer, in which an alignment sensor is mounted on the carriage together with the multiple print heads. According to this technique, automatic alignment is achieved through printout of predetermined patterns, automatic sensing of printout results, and calculation of alignment parameters. See U.S. application Ser. No. 08/901,560, "Auto-Alignment System For A Printing Device", the contents of which are incorporated herein by reference as if set forth in full.
One problem encountered in auto alignment techniques results from a back spray, or ink mist, that forms during the print process. Specifically, because the alignment sensor must be mounted in close proximity to the ink jet print heads, any ink mist that forms during the printing process tends to settle on the alignment sensor's face, obscuring light transmissivity and prevent accurate alignment.